A variety of print methods have been employed for imaging various sheet materials. Commonly employed print methods include gravure, off-set, flexographic, lithographic, electrographic, electrophotographic (including laser printing and xerography), ion deposition (also referred to as electron beam imaging (EBI)), magnetographics, inkjet printing, screen printing, and thermal mass transfer. More detailed information concerning such methods is available in standard printing textbooks.
Inkjet printing consists of individual ink drops deposited on the surface of the sheet. In order to achieve good image quality, the ink drops need to spread, join together, and form a substantially uniform, leveled film. Inkjet printing is emerging as the digital printing method of choice due to its good resolution, flexibility, high speed, and affordability. Inkjet printers operate by ejecting, onto a receiving substrate, controlled patterns of closely spaced ink droplets. By selectively regulating the pattern of ink droplets, inkjet printers can produce a wide variety of printed features, including text, graphics, holograms, and the like. The inks most commonly used in inkjet printers are water-based or solvent-based. Water-based inks require porous substrates or substrates with special coatings that absorb water.
However, ink compositions may comprise solvents that migrate through the sheet into an adhesive that is placed on the sheet opposite the inkjet image. This migration into the adhesive may have adverse effects on the adhesive properties. For example, the adhesive can become weak, causing the graphics to adhere poorly to a chosen substrate. This results in curling and lifting of the graphic from the substrate. In other embodiments, the bond between the adhesive and the sheet is compromised.